1. Technical Field
The present invention pertains to improvements in methods and apparatus for thermally treating surgically sterile liquid. In particular, the invention is an improvement of the methods and apparatus disclosed in U.S. Pat. No. 4,393,659 (Keyes et al), U.S. Pat. No. 4,934,152 (Templeton), U.S. Pat. No. 5,333,326 (Faries, Jr. et al). The disclosures in those patents are expressly incorporated herein in their entireties by this reference.
2. Discussion of the Prior Art
The Keyes et al patent discloses a surgical slush producing system having a cabinet with a heat transfer basin at its top surface. A refrigeration mechanism in the cabinet takes the form of a closed refrigeration loop including: an evaporator in heat exchange relation to the exterior of the heat transfer basin; a compressor; a condenser; and a refrigeration expansion control, all located within the cabinet. A separate product basin is configured to be removably received in the heat transfer basin. Spacers, in the form of short cylindrical stubs or buttons are arranged in three groups spaced about the heat transfer basin and projecting into the heat transfer basin interior to maintain a prescribed space between the two basins. During use, that space contains a thermal transfer liquid, such as alcohol or glycol, serving as a thermal transfer medium between the two basins. A sterile sheet of material, impervious to the thermal transfer medium, is disposed between the product basin exterior and the liquid thermal transfer medium to preserve the sterile nature of the product basin. Surgically sterile liquid, such as sodium chloride solution, is placed in the product basin and congeals on the side of that basin when the refrigeration unit is activated. A scraping tool is utilized to remove congealed sterile material from the product basin side to thereby form a slush of desired consistency in the product basin.
As noted in the Templeton patent, the above-described system has a number of disadvantages. In particular, the separate product basin must be removed and resterilized after each use. Additionally, the glycol or other thermal transfer medium is typically highly flammable or toxic and, in any event, complicates the procedure. The Templeton patent discloses a solution to these problems by constructing an entirely new apparatus whereby the product basin is eliminated in favor of a sterilized drape impervious to the sterile surgical liquid, the drape being made to conform to the basin and directly receive the sterile liquid. Congealed liquid is scraped off the sides of the conformed drape receptacle to form the desired slush.
In addition, Templeton also provides an electrical heater disposed at the bottom of the basin to convert the sterile slush to warmed liquid, or heat additional sterile liquid added to the basin. Templeton describes the need for such warm sterile liquid as occurring after a surgical procedure is completed to facilitate raising the body cavity of a surgery patient back to its normal temperature by contact with the warm liquid. However, there are a number of instances during a surgical procedure when it is desirable to have simultaneous access to both the sterile warm liquid and the sterile surgical slush. For example, if the surgical slush is not of the desired consistency (e.g., too thick), the availability of warm sterile liquid to be added to the slush permits rapid adjustability of the slush consistency. Likewise, maintaining instruments at or near body temperature during surgery is a desirable feature permitted by warm sterile liquid. Of course, if the warm sterile liquid is simultaneously available with the surgical slush, there is no need to wait for the slush to melt at the end of the surgical procedure. Finally, the simultaneous provision of slush and warm liquid permits the two to be comprised of different compounds as is sometimes necessary for various surgical procedures.
In response to the foregoing problems, the Faries Jr., et al U.S. Pat. No. (5,333,326) provides a thermal treatment system having a basin for containing warm surgical liquid placed adjacent a surgical slush basin of the type for example disclosed in the Templeton patent. The warming basin may be a separate unit secured to the pre-existing surgical slush unit, or may be constructed as part of an integral cabinet for the warming and cooling basins. A large surgical drape covers both of the basins and contains the warm liquid and the slush in a sterile manner. Alternatively, the thermal treatment system may include only the warming basin utilizing a drape to cover the basin and contain warm surgical liquid in a sterile manner. Generally, users of the aforementioned systems utilize the liquid in the warming basin to heat objects (e.g., medical instruments, containers) placed in the basin. However, placement of objects in the basin may puncture the drape in several different ways. For example, objects placed in the warming basin may trap air between the object base and drape material. The trapped air typically expands beneath the object when heated and expels the sterile liquid from beneath the object, thereby leaving the drape to absorb additional thermal energy from the basin at locations where liquid has been expelled. The additional thermal energy causes the drape to overheat, melt, and stick to the warming basin, thereby forming holes. Further, the drape material may soften significantly when exposed to the heated basin floor, thereby allowing normally safe (i.e., dull or blunt) objects to puncture the material (e.g., blunt plastic syringe tips and blunt tipped hemostats). Moreover, lack of sufficient liquid in the basin due to user error or evaporation tends to increase the amount of thermal energy absorbed by the drape, thereby causing portions of the drape to overheat forming hot spots and pinholes.